1. Field of the Invention
This invention relates generally to apparatus used in connection with the mooring of structures in offshore environments, and related methods of use. More specifically, this invention relates to a particular method for installation of a gravity installed anchor in a seabed and placement of a mooring assembly connected thereto, for connection of the anchor to a structure to be moored, and for later retrieval of the anchor, and to apparatus to carry out the method.
2. Description of the Related Art
This invention is directed toward a method for installation of a gravity installed anchor in a seabed and placement of a connected mooring assembly; connection of the anchor to a floating or submerged structure; and disconnection therefrom and retrieval of the gravity installed anchor from the seabed when no longer in use. Apparatus used in the method are also encompassed within the scope of the invention.
It is well known in the relevant art that various anchors are used to fix structures in place, in an offshore environment. Frequently, floating structures are fixed in place; for example, floating drilling rigs, production facilities, processing facilities, barges, work vessels, etc. In addition, mooring may be required for non-floating structures, such as pile-type structures which may be, to some greater or lesser degree, supported by the seabed, but which still require mooring.
It is also well known that various types of anchors are used to fix one end of a line to the seabed, such as dead weight anchors, clump anchors, embedment anchors, vertically loaded anchors, and a number of other designs.
The term “gravity installed anchor,” as used in this application, is used to refer to an anchor which achieves some degree of embedment in a seabed by virtue of a free fall (through the water) from a desired distance above the seabed, whereby the anchor penetrates a distance into the seabed. Such anchors can be used to moor floating structures, or to provide a fixing point for submerged structures. It is understood that the term “gravity installed anchor” is used broadly herein, and encompasses all types of anchors which can be installed into the seabed by virtue of a freefall through a water column, to and into the seabed.
In many mooring situations, it is desired to place the gravity installed anchor with a mooring line section or load line (e.g. a length of cable) already attached, said load line laid out on the seabed in the ultimate direction of the structure being moored (that is, substantially aligned with a line between the anchor location and the structure being moored), and, in some situations, with a subsea connector attached to the end of the load line distal from the gravity installed anchor. The present invention provides an efficient method of so placing a gravity installed anchor and a mooring assembly, and of its retrieval after use. In other applications, the gravity installed anchor may be installed with the entire mooring line attached, and with or without a subsea connector; in such applications, the end of the mooring line distal from the anchor (which may be laying on the seabed, or floating with a buoy) is picked up and connected to the structure being moored.